Stress-induced decrease in TRAF2 stability is mediated by Siah2

Abstract

TRAF2 serves as a central regulator of the cellular response to stress and cytokines through the regulation of key stress-signaling cascades. Here we demonstrate that wild-type, but not RING mutant, Siah2 targets TRAF2 for ubiquitylation and degradation in vitro. Siah2 mediates equally ef®cient ubiquitylation of RING mutant TRAF2. In vivo, Siah2 primarily targets TRAF2 for degradation under stress conditions. Tumor necrosis factor-a (TNF-a) and actinomycin D treatment results in accelerated TRAF2 degradation in wild-type mouse embryo ®broblasts (MEFs), as compared with Siah2 ±/± cells. Similarly, TRAF2 halflife is prolonged in Siah2 ±/± compared with wild-type MEFs subjected to stress stimuli. Siah2 ef®ciently decreases TNF-a-dependent induction of JNK activity and transcriptional activation of NF-kB. Apoptosis induced by TNF-a and actinomycin D treatment is increased upon expression of Siah2, or attenuated upon expression of TRAF2 or RING mutant Siah2. Identifying Siah2 as a regulator of TRAF2 stability reveals its role in the regulation of TRAF2 signaling following exposure to stress.

The ubiquitin ligase Siah2 regulates tumorigenesis and metastasis by HIF-dependent and -independent pathways

“…We next determined whether tumorigenesis and metastasis of melanoma cells would be affected upon inhibition of Siah2 ligase activity by a RING mutant (S2RM), a potent dominant-negative form of Siah2 (6). Stable expression of S2RM in SW1 cells (SW1 S2RM ) was confirmed in immunoblot analysis (Fig.…”

“…Somewhat similar to PHYL is Siahinteracting protein (SIP), which interacts with Siah within the same structural domain (3,4). In mammals, two isoforms, Siah1 and Siah2 (5), have been shown to control the stability of several substrates, including nuclear corepressor, ␤-catenin, TRAF2, ␣-ketoglutarate dehydrogenase, and prolyl hydroxylase 3 (PHD3), thereby affecting diverse cellular functions, such as signaling, survival, and mitochondrial biogenesis (6)(7)(8)(9)(10). We have demonstrated that by regulating PHD3 stability, Siah2 contributes to the abundance of hypoxia-inducible factor (HIF)-1␣, thereby playing an important role in the cellular response to hypoxia (9).…”

Role of NF-κB signaling in hepatocyte growth factor/scatter factor-mediated cell protection

“…Expression vectors for cIAP-1 and cIAP-2 were kindly provided by Dr John C. Reed (Burnham Institute, La Jolla, CA, USA) (Deveraux et al, 1998). The TRAF-2 expression vector was provided by Dr Ze'ev Ronai (Ruttenberg Cancer Center, Mount Sinai School of Medicine, New York, NY, USA) (Habelhah et al, 2002). Note that the substitution of an asparagine ( ¼ N) residue for the amino acid at position 17 of small GTPases Cdc42 and Rac1 (position 19 for Rho) reduces their affinity for GTP, thus creating dominant-negative mutants (Egan and Weinberg, 1993).…”

Phylogeny of the TRAF/MATH Domain

“…Interestingly, one of these proteins targeted by SIAH is TRAF2. Indeed, SIAH interacts with TRAF2 through its TD and catalyzes its ubiquitination and degradation under stress conditions 111 .…”